Are humans responsible for climate change?

Yes, humans are the primary cause of recent climate change (global warming since the Industrial Revolution). This is the overwhelming scientific consensus, based on multiple independent lines of evidence from observations, physics, paleoclimate records, and climate models.[1]

The Intergovernmental Panel on Climate Change (IPCC), in its Sixth Assessment Report (AR6, 2021), states: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” The likely range of total human-caused global surface temperature increase from 1850–1900 to 2010–2019 is 0.8°C to 1.3°C (best estimate 1.07°C), which accounts for essentially all the observed warming. Well-mixed greenhouse gases (mainly CO₂ from fossil fuels) contributed a warming of 1.0–2.0°C, partially offset by other human factors like aerosols (cooling of 0.0–0.8°C). Natural drivers (solar and volcanic) contributed only –0.1°C to +0.1°C, and internal variability –0.2°C to +0.2°C.[1]

Scientific Consensus

•Multiple studies of peer-reviewed literature find >99% agreement that humans are the main cause of recent climate change (e.g., a 2021 analysis of ~88,000 papers found consensus exceeding 99%, with only a handful of skeptical papers). Earlier work often cited ~97%.[2]

•Surveys of climate scientists show near-unanimous agreement (97–100%, higher among those most actively publishing on the topic). Leading scientific organizations worldwide (NASA, NOAA, AAAS, national academies, etc.) endorse this position.[3]

Key Evidence

Several reinforcing lines of evidence establish human responsibility:

1.Rising greenhouse gas concentrations from human activities: Atmospheric CO₂ has risen from ~280 ppm pre-industrially to over 410–420 ppm recently (with methane and nitrous oxide also up sharply). This increase is unequivocally from human sources—primarily burning fossil fuels, plus land-use changes like deforestation. Isotopic “fingerprints” (e.g., carbon isotopes) confirm the fossil-fuel origin, not natural sources like volcanoes or the ocean. Concentrations are higher than at any time in at least the last 800,000 years, and the rate of increase is unprecedented.[4]

2.Basic physics of the greenhouse effect: CO₂ and other GHGs trap heat (infrared radiation). This has been understood since the 19th century. Adding more GHGs amplifies the natural greenhouse effect, leading to surface warming.

3.Observed warming and changes match human fingerprints, not natural ones:

•Global surface temperature has risen ~1.1°C since the late 19th century (most since the mid-20th century), with oceans, atmosphere, and land all warming; ice melting; sea levels rising; and shifts in extremes (more heatwaves, heavy precipitation in many areas).

•Patterns include tropospheric warming + stratospheric cooling (expected from GHGs, opposite of what increased solar output would cause), ocean heat content increases, and specific regional/hydrological changes.

•Paleoclimate data (ice cores, tree rings, etc.) show the recent rate of warming is faster than natural variations over the past 2,000+ years (and much of the Holocene).[5]

4.Climate models and attribution studies: Models that include only natural forcings (solar variability, volcanoes) cannot reproduce the observed warming—they show little change or slight cooling. Models including human GHG emissions and other anthropogenic factors closely match observations. Detection-and-attribution studies quantify human influence as dominant.[6]

5.Ruling out alternatives: Solar irradiance has been stable or slightly declining in recent decades; volcanic activity does not explain the long-term trend; orbital cycles operate on much longer timescales. No known natural process accounts for the magnitude, rate, and pattern of recent changes.[7]

Human activities (fossil fuel combustion, agriculture, industry, land-use change) are the dominant driver. While Earth’s climate has always varied naturally, the current rapid warming is anthropogenic. This conclusion has strengthened over successive IPCC reports (from “discernible” influence in 1995 to “unequivocal” in 2021) and is supported by ongoing observations and research.[8]

For primary sources, see IPCC AR6 Working Group I (Physical Science Basis), NASA/NOAA climate pages, and peer-reviewed consensus studies.

Citations (8)

1ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/
Backs: “This is the overwhelming scientific consensus, based on multiple independent lines of evidence from observations, physics, paleoclimate records, and climate models.”
2cornell.eduAcademic
https://news.cornell.edu/stories/2021/10/more-999-studies-agree-humans-caused-climate-change
Backs: “Multiple studies of peer-reviewed literature find >99% agreement that humans are the main cause of recent climate change (e.g., a 2021 analysis of ~88,000 papers found consensus exceeding 99%, with only a handful of skeptical papers). Earlier work often cited ~97%.”
3nasa.govGovernment
https://science.nasa.gov/climate-change/scientific-consensus/
Backs: “Leading scientific organizations worldwide (NASA, NOAA, AAAS, national academies, etc.) endorse this position.”
4climate.govGovernment
https://www.climate.gov/news-features/climate-qa/what-evidence-exists-earth-warming-and-humans-are-main-cause
Backs: “Concentrations are higher than at any time in at least the last 800,000 years, and the rate of increase is unprecedented.”
5ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_03.pdf
Backs: “Paleoclimate data (ice cores, tree rings, etc.) show the recent rate of warming is faster than natural variations over the past 2,000+ years (and much of the Holocene).”
6royalsociety.orgAcademic
https://royalsociety.org/news-resources/projects/climate-change-evidence-causes/question-2/
Backs: “Detection-and-attribution studies quantify human influence as dominant.”
7nasa.govGovernment
https://science.nasa.gov/climate-change/causes/
Backs: “No known natural process accounts for the magnitude, rate, and pattern of recent changes.”
8cnrs.frNot yet classified
https://news.cnrs.fr/articles/long-standing-consensus-on-the-human-origin-of-global-warming
Backs: “This conclusion has strengthened over successive IPCC reports (from “discernible” influence in 1995 to “unequivocal” in 2021) and is supported by ongoing observations and research.”